This study investigated the effect of replacing margarine with red palm oil (RPO) in Zwieback on serum antioxidant and inflammation biomarkers in women with benign breast tumours. Using a double-blind, randomised controlled trial, 15 participants were divided into a control group (n = 8) and a treatment group (n = 7). The treatment group consumed Zwieback with RPO, providing 5.04 mg/day of β-carotene for eight weeks, while the control group received Zwieback without RPO. Results showed a significant increase (p<0.05) in SOD activity in both groups. A reduction of TNF-α, 8-isoprostane levels, and tumour size (p<0.05) was observed in the treatment group. However, the between-group difference in tumour size was not statistically significant after adjustment. The control group experienced a significant decline (p<0.05) in β-carotene levels. These findings suggest that adequate antioxidant intake, particularly β-carotene, may help maintain serum β-carotene levels and enhance antioxidant capacity. The consumption of Zwieback substituted with RPO may have beneficial effects on oxidative stress and inflammation, which are factors linked to cancer risk.